SOx concentration sensors for detecting the SOx concentration in exhaust gas have been known since the past. These known SOx concentration sensors normally use a solid electrolyte and are designed to measure the electromotive force generated by the change of SOx to sulfate ions so as to detect the SOx concentration in the exhaust gas (for example, refer to Japanese Patent Publication (A) No. 2004-239706).
However, there are the large problems that a conventional sulfur component detecting device using such an SOx concentration sensor will work only under high temperatures, the device becomes bulky, and in particular when the SOx concentration is low, it cannot detect the SOx concentration. Conventionally, as in this SOx concentration sensor, attention has been directed only at instantaneously detecting the SOx concentration. So long as trying to instantaneously detect the SOx concentration in such a way, various problems such as explained above will inevitably occur.
The inventors changed their thinking and turned their gaze to not instantaneously detecting the SOx concentration, but to detecting the cumulative amount of SOx exhausted over a long period. By changing their thinking in this way, they learned that it is possible to easily detect the amount of SOx in the exhaust gas—though the cumulative amount of SOx exhausted over a long period of time.
Note that the present invention may be applied most appropriately when detection of a cumulative amount of SOx exhausted over a long period of time is demanded. Further, even though it is unable to detect instant SOx concentrations, the present invention may be applied in cases where it is sufficient to be able to detect an average value of SOx concentration within a given fixed period or an average value of an exhausted amount of SOx in a given fixed period.